Power consumption estimation

ABSTRACT

A process for deriving a power transfer function of a circuit. The power transfer function can be used to represent the real time power consumption of a circuit based on the status of the inputs. In one embodiment, the power transfer function is derived from frequency domain analysis of signals applied to the inputs of a circuit during tests of the circuit. In one embodiment, the inputs of the circuit are grouped in groups based on a commonality of power consumption of the signals. The inputs may be grouped by clustering squared coherencies associated with the inputs. The transfer function may be implemented in a power monitoring circuit having inputs coupled to the inputs of the circuit to provide a real time estimation of power consumption of the circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to integrated circuits and morespecifically to power usage estimation for integrated circuits.

2. Description of the Related Art

It may be desirable for some applications to have a real time estimateof power consumption of an integrated circuit or of a portion of anintegrated circuit. Power consumption may be measured by measuring theamount of current being consumed. However such a method requires extracircuitry. Furthermore, it may not be possible to measure currentconsumption for a portion of an integrated circuit.

What is desirable is a system to provide a real time estimate of powerconsumption for at least a portion of a circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 sets forth one embodiment of a discrete time transfer functionand table illustrating concepts of how a transfer function can be usedfor power consumption estimation of a circuit according to the presentinvention.

FIG. 2 represents a block diagram of one embodiment of a method ofderiving a power transfer function which maps the input activity of acircuit to the power consumption of the circuit according to the presentinvention.

FIG. 3 is a block diagram of one embodiment of operation 207 of FIG. 2showing equations utilized for obtaining coherences from the results ofthe power characterization tests according to the present invention.

FIG. 4 shows one embodiment of clustering averaged squared coherenciesin two dimensional space according to the present invention.

FIG. 5 sets forth one embodiment of a block diagram of operation 211 ofFIG. 2 for deriving a power frequency response for each group of inputsaccording to the present invention.

FIG. 6 sets for one embodiment of equations according to the presentinvention.

FIG. 7 is a block diagram of a electronic system according to thepresent invention.

The use of the same reference symbols in different drawings indicatesidentical items unless otherwise noted.

DETAILED DESCRIPTION

The following sets forth a detailed description of a mode for carryingout the invention. The description is intended to be illustrative of theinvention and should not be taken to be limiting.

An impulse response is the consequence of an event over time. A transferfunction can be used to represent an impulse response. A power impulseresponse of an assertion (or other power consuming activity) of a signalat an input of a circuit represents the power consumed by a circuit overtime due to the assertion of that signal. A power transfer function canbe used to represent the power consumed over time by the assertion ofthe signal.

FIG. 1 sets forth a discrete time transfer function and tableillustrating concepts of how a transfer function can be used for powerconsumption estimation of a circuit. Equation 101 is an example of adiscrete transfer function which maps activity of groups of one or moreinput (e.g. g1, g2) of a circuit (not shown) to the total powerconsumption (Y_(T)) of the circuit based upon the activity of thosegroups of inputs. In the embodiment shown, each group represents a groupof inputs having similar power impulse response functions. Y_(g1)(T)represents an estimation of the component of the power consumptionY_(T)(T) from the activity of group g1 and Y_(g2)(T) represents anestimation of the component of the power consumption Y_(T) from theactivity of group g2.

The power impulse response for the group g1 inputs as represented bytransfer function 101, sets forth that 4 units of power are consumed inthe time period (T) that an input of group g1 is at a first state, and 2units of power are consumed in the next time period (T+1) due to theinput of group g1 being at the first state in time period (T). For theinputs of group g2, three units of power are consumed at the time period(T) when an input of group g2 is at a first state and one unit of poweris consumed two time periods later (T+2) due to the input of group g2input being at the first state at time period (T).

Table 103 illustrates an example of how transfer function 101 can beused to provide an estimate of the power consumed by a circuit duringtime periods T1-T8. A “1” in row g1 (T) or g2(T) represents that aninput of that group (g1 or g2) is at a first state during that timeperiod. The numbers in the rows of Y_(g1)(T) and Y_(g2)(T) represent thepower consumption at a particular time period due to the inputs of itsrespective group. Y_(T)(T) represents the total power consumed by acircuit at a particular time period.

As illustrated by table 103, a g1 input being at a first state at a timeperiod causes four units of power to be consumed during that time periodby the circuit and two units of power to be consumed in the next timeperiod (T+1). For example, at time T4, six units of power are beingconsumed by the circuit due to the inputs of group g1 (as shown in rowY_(g1)(T)), four units due to a g1 signal being at a first state at timeT4 and two units from a group 1 input being at a first state at time T3(as represented by the “₁” in row g1(T)).

For the embodiment of table 103, the inputs of g1 have two states, afirst state which causes the consumption of power by the circuit(indicated by a “1”), and a second state where no power is beingconsumed (as indicated by a “0”). In other embodiments, a circuit mayconsume power when the signal is at either state. In such embodiments,non zero numbers may appear in rows g1(T) and g2(T) to represent thesecond state. Also, transfer function 101 may include portionsrepresenting an impulse response from an input being in a second state.Furthermore, although not shown in table 103, more than one signal of agroup may be at the power consuming state during a time period. Forthose instances, the number in that row (e.g. g1(T) or g2(T)) wouldrepresent the number of signals of a group at that state.

With other embodiments, the inputs g1 and g2 as shown in table 103 mayrepresent another power consuming activity such as a change in state ofan input. Other embodiments may include a different number of inputgroups.

As can be seen from FIG. 1, a discrete time transfer function can beused to provide an indication of the power consumed by a circuit fromthe state (or other power consuming activity) of the inputs to thecircuit. Accordingly, such a transfer function may be used to provide anestimate of power usage of the circuit in real time based on the stateof the inputs. A

FIG. 2 represents a block diagram of one embodiment of a method ofderiving a power transfer function which maps the input activity of acircuit to the power consumption of the circuit. In one embodiment, thepower transfer function derived in method 201 is derived from theresults of tests run on a simulated circuit. However, in otherembodiments, a power transfer function may be derived from measurementsof an actual circuit (not shown).

With the method of FIG. 2, each input is placed into a group of inputsso as to simplify the derived power transfer function. The inputs aregrouped based on a commonality of power consumption of the circuitresponsive to signals applied to the inputs.

In 203, a first circuit block (not shown) of an integrated circuit isselected for deriving a power transfer function. In 205, at least onepower characterization test is run where signals are applied to theinputs of the circuit block to perform functions of the circuit block.In some embodiments, the signals applied are signals for performingnormal or expected operations of the circuit block. During the tests,the power consumption of the circuit block is recorded over time toproduce a power consumption log which shows the power consumed as afunction of time. In one embodiment wherein the transfer function isbeing derived from a circuit simulation, the circuit block is simulatedin VERILOG and the power consumption log is obtained from a gate levelpower analysis methodology.

In one embodiment, the power consumption log is a cycle by cycle powerconsumption profile of the circuit during the simulated tests. Thisprofile, in one embodiment, is obtained from a combination of profilesof the gate/macro external power consumption and profiles of gate/macrointernal power consumption. In one embodiment, profiles of thegate/macro external power consumption are derived from the switchingactivities of the nets that are connected to inputs and outputs of asimulated circuit during the tests and their associated netcapacitances. In one embodiment, the profiles of the gate/macro internalpower consumption are derived from the inputs and output of a simulatedcircuit using appropriate power models. In one embodiment, such powermodels are set forth in US patent application entitled “ModelingBehavior of an Electrical Circuit,” having Lipeng Cao as inventor,having a common assignee, having a filing date of Nov. 20, 2001, anapplication Ser. No. 09/989,325, and a publication number of US2003/0097348 A1, all of which is hereby incorporated by reference in itsentirety. The inputs of the power model are derived from switchingactivities of the nets of the tests and the associated net capacitancesof the inputs and outputs of the simulated circuits. In one embodiment,the models provide representations of both dynamic power consumption andleakage power consumption.

In 207, for each power characterization test, an average squaredcoherency between each input of the circuit and the power consumed bythe circuit as indicated by the power consumption log is derivedmathematically from the Fourier transforms of the signals applied to theinputs over time during the test and the Fourier transform of the powerconsumption as indicated by the power consumption log.

In 209, the inputs having a commonality of power consumption are groupedinto groups. In one embodiment of 209, the inputs are grouped byclustering the average squared coherencies. In one embodiment, theaverage squared coherency for each input from each test is clustered inmulti dimensional space having a dimension for each test run. In oneembodiment, commonality of power consumption of the circuits for theinputs is determined by the proximity of the averaged squaredcoherencies in the multidimensional space.

FIG. 4 shows one example of clustering averaged squared coherencies intwo dimensional space 401. Two dimensional space 401 is utilized forclustering the average squared coherency for data from two powercharacterization tests. The average squared coherencies shown in FIG. 4are derived from two power characterization tests on a circuit (notshown) having inputs A, B, C, D, E, and F. C_(A1), C_(B1), C_(C1),C_(D1), C_(E1), and C_(F1) (as shown on the Y axis) represent theaverage squared coherencies with respect to power consumption derivedfor inputs A, B, C, D, E, and F for a first power characterization testand C_(A2), C_(B2), C_(C2), C_(D2), C_(E2), and C_(F2) (as shown on theX axis) represent the average squared coherencies with respect to powerderived for inputs A, B, C, D, E, and F for a second powercharacterization test. C_(AT), C_(BT), C_(CT), C_(DT), C_(ET), andC_(FT) represent the total averaged squared coherency of both test casesin multidimensional space 401. In the embodiment shown, the inputs aregrouped for commonality by the proximity of the average squaredcoherencies to one another in the two dimensional space. Inputs A and Bare grouped in group 1, inputs C and E are grouped in group 2, andinputs D and F are grouped together in group 3. Depending upon theproximity requirements for a group, Some groups may have only one inputdepending upon the proximity of its average squared coherency to theother average squared coherencies.

Referring back to FIG. 2, in 211, a frequency response function betweenthe power consumed by the circuit and each group is derived. In 213,power impulse response functions for each group are derived from thefrequency response functions derived in 211. In 215, a power transferfunction is mathematically derived from the impulse response functionsderived in 213. This derived power transfer function includes a modelfor each group of inputs. Each model is derived from the impulseresponse function derived for each group of inputs. Each model includesa formula with adjustable coefficients of initial values. In 217, thecoefficients are further adjusted using conventional non linearoptimization techniques such as BFGS (Broyden, Flechter, Goldfarb, andShannon), a quasi-Newton algorithm.

Referring to FIG. 6, equation 605 sets forth an example of a transferfunction for a circuit having two groups of inputs (g1 and g2). “B” inequation 605 represents a delay operator which has the effect ofdelaying the quantity for one time period. The designations a, b, c, andd in 605 are adjustable coefficients. The model for group g1 in equation605 is a first order discrete transfer function (a/(1+bB)) and the modelfor group g2 is a 0 order discrete transfer function (c+dB). Models ofother orders of transfer functions in rational function polynomialformats may be used in other embodiments. The model used for each groupis based on the impulse response function for each group derived in 213.In some embodiments, the impulse response function is used to identifythe type and number of parameters in the rational function. Non lineartechniques may be used to evaluate the value of the parameters.

Referring back to FIG. 2, in 219, the derived power transfer functionwith the adjusted coefficients is validated. In one embodiment, thepower transfer function is validated by comparing the results of a powerconsumption estimation from the power transfer function with the powerconsumption as measured in the power consumption logs. In anotherembodiment, the results of the power consumption estimation can becompared with laboratory test results obtained from an actual circuit.If the validation results are not satisfactory (e.g. % 10 or less), insome embodiments, the inputs in 209 may be regrouped and operations 211through 219 are repeated. In other embodiments, if the validationresults are not satisfactory, the coefficients of the power transferfunction may be readjusted in 217 and operation 219 is repeated. Stillin other embodiments, new models may be utilized in 215 with operations217 and 219 repeated.

If the circuit block is part of a larger circuit, then in 221, validatedtransfer functions are obtained for other circuit blocks of the circuitutilizing operations 203-219 as shown in FIG. 2.

FIG. 3 is a block diagram of one embodiment of operation 207 showingequations utilized for obtaining coherences from the results of thepower characterization tests. In 303, a Fourier transform (equation 313)is made for each signal applied to an input for each test to convertthat signal to the frequency domain. A Fourier transform (equation 315)is made of each power consumption log for each test to convert thoselogs into the frequency domain. In FIG. 3, X represents an input, and Yrepresents power.

In 307, each Fourier transform of a signal applied to an input (obtainedin 303) is used to derive an autoperiodgram (I_(xx)(f)) (equation 317)for an input for each test. Also, the Fourier transform of each powerconsumption log of each test is used to derive an autoperiodgram(I_(yy)(f)) (equation 319) for the power consumed for each test.Additionally in 307, for each test, the Fourier transform of a signalapplied to an input and the Fourier transform of the power consumptionlog are used to derive a cross periodgram (I_(xy)(f)) for each input ofthe circuit (see equation 321). In 309, for each input of each test, asquared coherency (which is a function of frequency (f)), is derivedusing the results derived in 307 (see Equation 323). As shown in 309,each squared coherency is a value between 0 and 1. In 311, for eachinput of each test, the squared coherency is averaged over allfrequencies to obtain an average squared coherency of the input withrespect to power. In other embodiments, the squared coherency isaveraged over selected frequency bands. See FIG. 4 showing the averagesquared coherencies for test 1 located on axis Y and showing theaveraged squared coherencies for test 2 on axis X.

FIG. 5 sets forth a block diagram of operation 211 for deriving a powerfrequency response function for each group of inputs. In 501, thesignals applied to each input of a group for all tests are combined tomake one signal. This may be performed by attaching “end to end” thesignals applied to an input from each test to make one combined signal.The combined signals of each input of a group are then averaged togetherto make a combined group signal. In 502, the power logs for the testsare combined to make a combined power consumption log. The powerconsumption logs are attached “end to end” in the same order as thesignals applied to the input. In 503, a Fourier transform of eachcombined group signal is derived (with an equation similar to equation313), to convert each of the combined group signals to the frequencydomain. Also, a Fourier transform for the combined power consumption logis also derived (see equation 315) to convert the combined powerconsumption log to the frequency domain.

In 505, for each group, an autoperiodgram of each combined group signalis derived from the Fourier transform of the combined group signal (seeequation 317). Also in 505, a crossperiodgram between each input groupwith respect to the other input groups is derived from the Fouriertransforms of the combined group signals. Further in 505, for eachgroup, a cross periodgram (see e.g. equation 323) between each group andpower is derived from the Fourier transform of the combined power logand the Fourier transfer of a combined group signal.

In 507, the frequency response function with respect to power for eachinput group is calculated by solving linear equations 601 of FIG. 6.H₁(f) represents frequency response function for input group one withrespect to power. H₂(f) represents the frequency response function forthe second input group. Referring to equation 601, I_(x1x1)(f)represents the autoperiodgram for the first input group (derived in505). I_(x1x2)(f) is the cross periodgram between the first input groupand the second input group (derived in 505). I_(x1y)(f) is thecrossperiodgram for input group 1 and power.

Referring back to FIG. 2, as stated earlier, in 213, a power impulseresponse function for each input group is derived from the frequencyresponse function for the input group using equation 603 wherein V_(k)represents the power impulse response function for each group. As statedearlier, each power input response function is then used tomathematically derive a portion of the transfer function for the circuitblock in 215.

Because in some embodiments, the inputs may be grouped according to acommonality of power consumption, the power transfer function derivedmay be less complex than a transfer function which would include a modelfor each signal. Accordingly, grouping the inputs may allow for thepower consumed to be estimated by a relatively “less complex” transferfunction. However, in some embodiments, each signal may have its ownmodel in a transfer function.

In other embodiments, the averaged squared coherencies may be analyzedby other conventional methods to determined a commonality of powerconsumption of the circuit for the inputs. For example, in someembodiments, the power consumption logs and input signals may be placedback to back to obtain one long test, wherein a single average squaredcoherency is obtained for each input. The inputs are grouped based upontheir proximately of the average squared coherency values.

The derived power transfer function may be utilized for power debugginga designed circuit. For example, a derived transfer function may be usedto identify areas for detailed examination of power consumption,evaluate clock efficiency, identify fundamental modes of powerconsumption for specific circuits of an integrated circuit, and evaluatethe power gain of net clusters through transfer functionrepresentations. Also the transfer functions may be used to performlarge scale mixed mode power simulations. Such transfer functions mayalso be used for high level power planning and budgeting.

The derived power transfer function may also be utilized to predictpower consumption in real time. A transfer function may be implementedin an electronic system to provide an indication of the power beingconsumed by a circuit of the electronic system. Such an indication maybe used to provide the electronic system with real time powerestimations to enable the electronic system to perform power monitoringand/or power management functions.

FIG. 7 is a block diagram of a electronic system according to thepresent invention. System 701 includes a first integrated circuit 703and a second integrated circuit 705. As an example, electronic system701 may be one of e.g. a computer system, a cellular phone, other typeof wireless device, or other type of electronic system.

Integrated circuit 703 includes circuits 709, 711, and 713 which performvarious operations for system 701. In one embodiment, integrated circuit703 is a microcontroller where circuit 709 is a memory, circuit 711 is aprocessor core, and circuit 713 is a bus controller. Integrated circuit703 also includes a power monitor circuit (715, 717, and 719) associatedwith each circuit (709, 711, and 713). Power monitor circuits 715, 717,and 719 implement a power transfer function for its associated circuit.In one example, the power transfer functions are derived by a methodsimilar to the method set forth in FIG. 2.

Each power monitor circuit has inputs coupled to the inputs of itsassociated circuit. Each power monitor circuit has at least one outputfor providing an indication of an estimate of the power being consumedby its associated circuit based upon the signals being applied to theinputs of its associated circuit. In one embodiment, the indication isin digital form. In other embodiments, the indication may be in analogform.

In FIG. 7, the outputs of each power monitor circuit (715, 717, and719),provides an indication of the power consumed by a circuit block forwhich a power transfer function was derived by a method similar to thatshown in FIG. 2. In other embodiments, the output of each power monitorcircuit (715, 717 and 719) provides an indication of the power consumedby a multiple circuit blocks, each of which a power transfer functionwas derived by a method shown in FIG. 2. In such embodiments, thetransfer functions from each circuit block are combined such that theoutputs of the power monitoring circuits are indicative of the powerconsumed by all of the circuit blocks of the associated circuit. In oneembodiment, the transfer functions are implemented in the power monitorcircuit with an analog filter circuit such as e.g. a switched capacitorcircuit.

In another embodiment, the transfer functions are implemented in thepower monitor circuits with digital filters.

As shown in FIG. 7 each power monitor circuit can either be coupled toprovide an indication of power consumption estimation to an on chipcontroller 707 or coupled to provide the indication to an off chipcontroller 706. In some embodiments, on chip controller (707) maycombine information from the various power monitor circuits and providethat information to an off chip controller.

Either of these controllers (707, 706) may utilize the power consumptioninformation to control the operation of the components of system 701 tomanage the power consumption of electronic system 701. In oneembodiment, system 701 is managed such that it consumes only a limitedamount of power at any one time. In such a system, certain operations(e.g. accessing a hard drive, transmitting information, performingdecoding operations) may be delayed until the power consumed by thecircuits (as indicated by the outputs of power monitor circuits 715, 717and 719) is below a particular threshold.

In other embodiments, the power consumption information may be used forload shedding to reduce power consumption during low power modes (e.g.during a low battery mode). Furthermore, the power consumptioninformation may be used to provide a more accurate estimation of theamount of battery power remaining, in that actual power consumed can bemonitored.

Furthermore, because, the transfer functions use delay operators, thepower monitoring circuits may be used to provide a forecast of powerconsumption. Such information may also be used for various powermanagement techniques.

Because the power monitoring circuits 715, 717, and 719 implementtransfer functions having models representing groups of inputs, thecomplexity of the power transfer function may be reduced, therebyreducing the complexity of a power monitor circuit whose outputs provideand indication of the power consumed. In other embodiments, the powermonitor circuit may be located off chip from its associated circuit.

In one aspect, the invention includes a method of deriving a powertransfer function of a circuit. The method includes running at least onetest on a circuit having a plurality of inputs to obtain information onpower consumption of the circuit responsive to signals applied to theplurality of inputs. The method also includes grouping the plurality ofinputs into groups of at least one input based on a commonality of powerconsumption of the circuit for the plurality of inputs as determinedfrom the information. The method further includes deriving a powertransfer function for providing an estimate of power consumption of thecircuit responsive to signals applied to the plurality of inputs of thecircuit. The transfer function includes a portion for each group of thegroups.

In another aspect of the invention, an apparatus includes a circuithaving a plurality of inputs and a power monitor circuit coupled to theplurality of inputs. The power monitor circuit implements a powertransfer function. The power monitor circuit has at least one output forproviding an indication representative of power consumed by the circuitbased upon signals applied to the plurality of inputs.

In another aspect, the invention includes a method of deriving a powertransfer function of a circuit. The method includes running at least onetest on a circuit having a plurality of inputs to obtain information onpower consumption of the circuit responsive to signals applied to theplurality of inputs. The method also includes deriving at least onepower impulse function from the information. Each power impulse responseof the at least one power impulse response is representative of at leastone input of the plurality of inputs. The method also includes derivinga transfer function from the at least one power impulse function.

While particular embodiments of the present invention have been shownand described, it will be recognized to those skilled in the art that,based upon the teachings herein, further changes and modifications maybe made without departing from this invention and its broader aspects,and thus, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention.

1. A method of deriving a power transfer function of a circuit, themethod comprising: running at least one test on a circuit having aplurality of inputs to obtain information on power consumption of thecircuit responsive to signals applied to the plurality of inputs;grouping the plurality of inputs into groups of at least one input basedon a commonality of power consumption of the circuit for the pluralityof inputs as determined from the information; deriving a power transferfunction for providing an estimate of power consumption of the circuitresponsive to signals applied to the plurality of inputs of the circuit,wherein the transfer function includes a portion for each group of thegroups.
 2. The method of claim 1 wherein the grouping comprises:deriving at least one coherency for each input of the plurality withrespect to power consumption based on the information; clustering thecoherencies to identify the groups.
 3. The method of claim 2 wherein thederiving at least one coherency further includes: deriving, for eachinput of the plurality and for each test of the at least one test anaverage squared coherency; wherein the clustering the coherenciesfurther includes clustering the average squared coherencies.
 4. Themethod of claim 2 wherein the deriving at least one coherency furtherincludes: taking a Fourier transform applied of each signal applied toeach input of the plurality for each test of the at least one test;taking a Fourier transform of the power consumed for each test of the atleast one test; wherein a coherency of the at least one coherency foreach test is derived from the Fourier transform of the signal applied tothe input for that test and the Fourier transform of the power consumedfor that test.
 5. The method of claim 2, wherein the clustering thecoherencies comprises clustering in multi-dimensional space having adimension for each test of the at least one test.
 6. The method of claim1, wherein the power transfer function includes coefficients, whereinthe deriving the power transfer function further includes: determiningan accuracy of the transfer function; and changing the coefficients toimprove the accuracy of the power transfer function.
 7. The method ofclaim 1 wherein each portion implements a model, wherein the derivingthe power transfer function further includes: deriving, for each groupof at least one input, an impulse response function between the signalsand the power consumption; deriving a model for each group from theimpulse response function derived for that group.
 8. The method of claim7 wherein the deriving the power transfer function further includes:deriving, for each group, a frequency response function; wherein theimpulse response function for each group is derived from the frequencyresponse function for the group.
 9. The method of claim 8 wherein thederiving for each group of at least one input a frequency responsefunction further includes: combining the signals for each test of the atleast one test applied to the inputs of each group to form a combinedsignal for each group; taking a Fourier transform of the combined signalfor each group and a Fourier transform of the power consumed during theat least one test; deriving, for each group of inputs, anautoperiodgram, a cross periodgram between the group and each of theother groups, and a cross periodgram between the group and the powerconsumed from the Fourier transform of each combined signal and theFourier transform of the power consumed; solving linear equationsincluding the autoperiodgram, the cross periodgram between the group andeach of the other groups, and a cross periodgram between the group andthe power consumed for each group to derive the frequency impulsefunction for each group.
 10. The method of claim 1 further comprising:implementing the power transfer function in a second circuit wherein thesecond circuit includes inputs coupled to the inputs of the circuit. 11.A method of claim 1 further comprising: running at least one test on asecond circuit having a plurality of inputs to obtain information onpower consumption of the second circuit responsive to signals applied tothe plurality of inputs of the second circuit; grouping the plurality ofinputs of the second circuit into groups of at least one input of thesecond circuit based on a commonality of power consumption of the secondcircuit for the plurality of inputs as determined from the information;deriving a second power transfer function for providing an estimate ofpower consumption of the second circuit responsive to signals applied tothe plurality of inputs of the second circuit, wherein the second powertransfer function includes a portion for each group of the groups of thesecond circuit.
 12. The method of claim 1 further comprising: simulatingthe circuit; wherein the running at least one test on the circuitincludes running the at least one test on the simulated circuit.
 13. Themethod of claim 1, wherein the circuit is a circuit of an integratedcircuit, the method further comprising: deriving a second transferfunction for providing an estimate of power consumption for a secondcircuit, wherein the second circuit is a circuit of the integratedcircuit and has a plurality of inputs; implementing the first transferfunction as a first power monitoring circuit on the integrated circuit,wherein the first power monitoring circuit has a plurality of inputscoupled to the plurality of inputs of the first circuit; andimplementing the second transfer function on the integrated circuit as asecond power monitoring circuit on the integrated circuit, wherein thesecond power monitoring circuit has a plurality of inputs coupled to theplurality of inputs of the second circuit.
 14. The method of claim 1wherein the deriving includes performing frequency domain. analysis ofthe information.
 15. The method of claim 1 wherein the grouping includesperforming frequency domain analysis of the information.
 16. Anapparatus comprising: a circuit having a plurality of inputs; a powermonitor circuit coupled to the plurality of inputs, the power monitorcircuit implementing a power transfer function, the power monitorcircuit having at least one output for providing an indicationrepresentative of power consumed by the circuit based upon signalsapplied to the plurality of inputs.
 17. The apparatus of claim 16wherein the circuit and the power monitoring circuit are implemented inan integrated circuit.
 18. The apparatus of claim 17 wherein theintegrated circuit includes at least one external terminal forexternally providing the indication.
 19. The apparatus of claim 16wherein the indication has a digital form.
 20. The apparatus of claim 16further comprising: a second circuit having a second plurality ofinputs, and a second power monitor circuit coupled to the secondplurality of inputs, for a providing a second signal representative ofpower consumed by the second circuit based upon signals applied to thesecond plurality of inputs.
 21. The apparatus of claim 20 wherein thecircuit, the second circuit, the power monitor circuit and the secondpower monitor circuit are implemented in an integrated circuit.
 22. Theapparatus of claim 16 wherein each input of the plurality of inputsbelongs to a group of at least one input of a plurality of groups,wherein the power transfer function includes a portion for each group ofthe plurality.
 23. The apparatus of claim 22 wherein each portionincludes a model based on a representative power impulse function of thegroup.
 24. The apparatus of claim 22 wherein the inputs of each group ofthe plurality have a commonality of power consumption of the circuit.25. The apparatus of claim 16, further comprising a second circuit forreceiving the indication.
 26. The apparatus of claim 25 wherein thecircuit and the second circuit are each implemented on an integratedcircuit.
 27. The apparatus of claim 16 wherein the power monitor circuitincludes filter circuit, wherein the transfer function is implemented inthe filter circuit.
 28. The apparatus of claim 27 wherein the filtercircuit is an analog filter circuit.
 29. The apparatus of claim 28wherein the analog filter circuit is a switched capacitor circuit. 30.The apparatus of claim 28 wherein the filter circuit is a digital filtercircuit.
 31. A method of deriving a power transfer function of acircuit, the method comprising: running at least one test on a circuithaving a plurality of inputs to obtain information on power consumptionof the circuit responsive to signals applied to the plurality of inputs;deriving at least one power impulse function from the information,wherein each power impulse response of the at least one power impulseresponse representative of at least one input of the plurality ofinputs; deriving a transfer function from the at least one power impulsefunction.
 32. The method of claim 31 wherein the deriving includesperforming frequency domain analysis of the information.
 33. The methodof claim 31 further comprising: implementing the power transfer functionin a second circuit wherein the second circuit includes inputs coupledto the inputs of the circuit.